Softshell blood reservoirs are commonly used in cardiac surgery to store blood in the blood circuit of a heart-lung machine. Traditionally, the blood inlet and outlet tubing is formed integrally with the softshell reservoir. In use, the perfusionist hangs up the reservoir, unrolls the tubing, trims it as necessary, and connects it to the blood source or sources and to the pump inlet of the heart-lung machine.
Some softshell reservoirs have two inlets: one for venous blood and one for cardiotomy blood. Others have only one; these are used where venous and cardiotomy blood are already mixed upstream of the softshell reservoir. Both types of reservoirs are typically asymmetrical in design, and the blood inlets and outlet are on opposite sides of the reservoir's central vertical axis. Although the reservoir can be reversed in some instances, depending upon the mounting hardware, conventional reservoirs are typically designed for a specific position with respect to the heart-lung machine. In practice, however, the layout of the operating room may dictate a different position; i.e. the reservoir needs to be positioned sometimes on the perfusionist's right, sometimes on his left, depending upon the circumstances. This can at times be awkward by causing the inlet and outlet tubing to cross each other and interfere with sampling or other activities. It also potentially increases the length of the tubing. The latter is clinically meaningful, because it is necessary for the well-being of the patient to keep the saline priming volume of the blood circuit (of which the tubing is a part) at an absolute minimum.